$5$ moles of $\mathrm{A}{\mathrm{B}}_2$ weigh $125\times {10}^{-3}\mathrm{ }\mathrm{k}\mathrm{g}$ and $10$ moles of ${\mathrm{A}}_2{\mathrm{B}}_2$ weigh $300\times {10}^{-3}\mathrm{ }\mathrm{k}\mathrm{g}$ . The molar mass of A $\left({\mathrm{M}}_{\mathrm{A}}\right)$  and molar mass of     $\mathrm{B}\left({\mathrm{M}}_{\mathrm{B}}\right)$  in $\mathrm{k}\mathrm{g}\mathrm{ }{\mathrm{m}\mathrm{o}\mathrm{l}}^{-1}$ are:

In the following reaction:

$\mathrm{A}+2\mathrm{B}+3\mathrm{C}\rightleftharpoons \mathrm{A}{\mathrm{B}}_2{\mathrm{C}}_3$
$6.0 \mathrm{g}$ of $\mathrm{A}$, $6.0\times {10}^{23}\mathrm{ }$ atoms of $\mathrm{B}$ and $0.036 \mathrm{mol}$ of $\mathrm{C}$ reacted and formed $4.8 \mathrm{g}$ of compound $\mathrm{A}{\mathrm{B}}_2{\mathrm{C}}_3$. If the atomic mass of $\mathrm{A}$  and $\mathrm{C}$ are $60$ and $80 \mathrm{amu}$, respectively. What is the atomic mass of $\mathrm{B}$ in $\mathrm{amu}$? (Avogadro number$=6\times {10}^{23}$)

The number of atoms in $8 \mathrm{g}$ of sodium is $x\times {10}^{23}.$ The value of $x$ is _____ . (Nearest integer)

$\left[\text{ Given : }{\mathrm{N}}_{\mathrm{A}}=6.02\times {10}^{23}{ \mathrm{mol}}^{-1}\right.\text{ Atomic mass of }\mathrm{Na}=23.0\mathrm{u}]$